Biological and immunological properties of ocular components were examined. Retinal rod outer segments (ROS) were found to be highly inhibitory to lymphocyte cultures. These inhibitory effects were found to be mainly due to the oxidizing activity of the ROS preparations (perhaps by the release of free radicals), since the inhibition could be averted by anti-oxidants like vitamin E or 2-mercaptoethanol. Two components of ROS, retinol and docosahexaenoic acid, had similar inhibitory effects. ROS were not inhibitory to macrophage cultures but, rather, were readily phagocytized by these cells. Rabbits immunized with rat lens extracts responded with a dissociated immune response: serum antibodies reacted mainly against the organ-specific proteins (crystallins) from various species, while the cellular immune response was directed mainly against the species-specific antigens.